1. Field of the Invention
The present invention relates generally to a stimulating medical device and, more particularly, to pharmaceutical agent delivery in a stimulating medical device.
2. Related Art
Medical devices having one or more implantable components, generally referred to as implantable medical devices herein, have provided a wide range of therapeutic benefits to patients over recent decades. As such, the type of implantable devices and the range of functions performed thereby have increased over the years. Particular types of implantable medical devices, referred to as stimulating medical devices, are used to stimulate the nerve cells of the device recipient. A notable use for such stimulating medical devices is in recipients who suffer from various forms of hearing loss.
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person suffers from hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the cochlea, and thus the sensory hair cells therein, are impeded, for example, by damage to the ossicles. Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. Acoustic hearing aids stimulate an individual's cochlea by providing an amplified sound to the cochlea that causes mechanical motion of the cochlear fluid.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from some forms of sensorineural hearing loss are thus unable to derive suitable benefit from conventional acoustic hearing aids. As a result, hearing prostheses that apply electrical stimulation signals to nerve cells of the recipient's auditory system have been developed to provide the sensations of hearing to persons whom do not derive adequate benefit from conventional hearing aids. Such electrically-stimulating hearing prostheses apply electrical stimulation to nerve cells of the recipient's auditory system thereby providing the recipient with a hearing percept.
As used herein, the recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and parts of the brain used to sense sounds. Hearing prostheses that apply electrical stimulation signals to the recipient include, for example, auditory brain stimulators and cochlear prostheses (commonly referred to as cochlear prosthetic devices, cochlear implants, cochlear devices, and the like; simply “cochlear implants” herein.)
Oftentimes sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which transduce acoustic signals into nerve impulses. It is for this purpose that cochlear implants have been developed. Conventional cochlear implants provide a recipient with a hearing percept by delivering electrical stimulation signals directly to the auditory nerve cells, thereby bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use an electrode array implanted in the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound.